The present invention relates generally to assaying the condition or degradation of an oil, such as lubricating oil, hydraulic fluid, synthetic oil, animal oil, vegetable oils, and more particularly to a fluorescent titration method for determining the amount of total hydrogen ion activity present in a substantially non-aqueous oil as an indication of degradation of the oil.
Lubricating oil serves several purposes in an engine or other mechanical device. These oils play the role of coolant, lubricant, and dispersant. When functioning as a dispersant, combustion by-products, wear debris, and degradation products are suspended in the oil, neutralized by sacrificial oil additives, or both.
It is well known that the life expectancy of internal combustion engines are heavily influenced by the rate of wear of lubricated surfaces. When good lubricating oil quality is maintained, the useful life expectancy of the engine is significantly increased. However, if an engine is run for extensive periods of time with oil that has become heavily degraded, excessive wear may occur in the engine, thereby decreasing the engine's useful life.
Although most engine users realize that engine life is directly tied to maintaining good oil quality, there is much less certainty concerning what is good oil quality and how good oil quality should be maintained. Most engine manufacturers recommend fixed oil change schedules based on elapsed time, elapsed vehicle miles or elapsed hours of oil use. However, it is well known that oil life is a function of operating conditions, weather, engine conditions, and time-in-use, as opposed to a fixed mileage or time.
These engine manufacturers suggested oil change periods are based on figures which make assumptions about operating factors such as fuel quality, engine loading, and operating environment. While these suggested periods are based on figures that would include average operating conditions, there are a large number of operators, such as the military, railroads and fleet operators, whose operating conditions do not fall within the parameters of the engine manufacturer. In such instances, it is desirable to rely on periodic in-service oil analysis rather than fixed oil change intervals so that oil is changed only when it is degraded.
It has long been recognized that the degradation of oils involves the oxidation of the oil's various components, and as the oil becomes more degraded, there is less protection available for the engine. This degradation process involves chemical changes in the composition of the oil leading to an increase ultimately in the acidity of the oil. As a precautionary measure, lubricating oil manufacturers typically add a base package to the oil to neutralize acids formed from oil degradation. Over time, however, the base package is depleted leading to a lower total base number ("TBN") and a higher total acid number ("TAN") in the oil. This accumulation of acids leads to increased wear rates of the metal components of the engine. If left unchecked, premature mechanical failure will result. New smaller high output engines are even more damaging to the oil, resulting in faster depletion of the additive base package.
There is a direct correlation between the acid contents in the oil and the amount of oil degradation. The higher acid content of the oil, the greater the oil degradation. Another factor is the contamination of the oil with water, acid and sludge that results primarily from piston ring and valve guide blow-by. Together these two factors ultimately produce acidic oil which should be changed in order to afford maximum protection for the engine.
One known method for monitoring the degradation of engine oil involves obtaining a sample of the oil and transporting the sample to a laboratory for analysis. While such a method can correctly analyze certain factors, such as flash point, pour point, ppm of wear metals, viscosity, sulfated ash content, TBN and TAN, the time delays involved in obtaining results make this method unsatisfactory for determining oil change time, particularly when the engine is located at a remote location from the laboratory.
One standard method for determining the acidity of oil is set forth in the American Society of Testing Materials Standard Test Method D 974. This titration method has been widely used to indicate the relative changes that occur in an oil during use under oxidizing conditions and reports these changes in terms of relative changes in neutralization numbers known as the TAN and the TBN. Compounded engine oils can and usually have both acid and base numbers in this test.
Another method, described in U.S. Patent No. 4,793,977, involves a colorimetric detector for qualitatively monitoring oil degradation. The reference discloses that the detector can be prepared from three chemical reagents: a polymeric matrix, one or more indicator dyes, and a basic compound bound to the matrix. The ionomers are polymers which have water tightly bonded thereto. A dye, which has a net charge opposite to that of the matrix, is bonded to the ion-rich domains of the ionomer. The detector is prepared by soaking the ionomers in a solution of dye or dyes to produce chromogens. Then, the dyed ionomer matrix is soaked in strong base. Afterward, the detectors are air dried. Soaking the detectors so prepared into hot (100.degree. C.) oil gives a color change if the hot oil is acidic. Because of the construction of the detector, the method disclosed detects acid in an aqueous microenvironment.
There is a need to be able to quickly and accurately determine the total hydrogen activity in oil to allow timely oil changes or supplementation of the oil additive package on the basis of need and not at an arbitrary interval set by the manufacturer. Current methods for the determination of acid in non-aqueous solutions such as potentiometric and colorimetric titrations are time consuming and require a great deal of operator training while giving a reasonable level of accuracy. Other methods are capable of giving only qualitative, not quantitative, data. The desirable method for the determination of the level of acid, as the total hydrogen activity, in oil must be fast, accurate, and require only a low level of operator training. The method must preferably give quantitative results.
There is also a need to be able to quickly and accurately determine the total hydrogen activity in a frying oil used in a restaurant to allow timely oil changes.